Well, there is a game that has a system that works like this, according to their website:

"The World
Strategically, a given world is divided into a 200 x 150 grid map. Each grid represents a single province (assuming it’s land).

Provinces that are not surrounded by friendly territory can become contested at a rate of up to 25% of the player’s total territory per day. For example, if a player’s territory is a single long line of 9 territories, then any 2 of them can become contested per day. However, if that same player’s society is shaped in a 3 x 3 grid, the center most province cannot become contested because it is surrounded by friendly territories.

Moreover, players can also join up with other players to form empires. Territories controlled by someone in the same empire are counted as friendly territories.

If someone attacks one of your provinces while you are not on-line, someone from your empire can take control of your forces (players can also set which members of the empire have this privilege or can set a certain imperial points threshold) to defend your province. If they are successful, they can win imperial points which help them gain standing in the empire and provide other bonuses. If no one is available to defend your society while you’re off-line, the computer AI will be quite effective at doing it.

Border provinces can be fortified with expeditionary forces and defensive structures so that they are more defensible during the player’s absence."

I will not say what game this is because I am not sure if I am allowed, since it could be considered advertising.